Changes of the Upper Airway Volume After Orthognathic Surgery

Background Orthognathic surgery affects the position of the teeth and jaws. The upper airway compartment is in close approximation to these tissues. Consequently, changes of the respiratory volume after surgical treatment in this region is expected.

Orthognathic surgery The correction of severe malocclusions and dentofacial deformities has since the beginning of 20th century been treated with orthodontic and surgical methods. Epidemiologic surveys reveal that about 5 % of the western population has dentofacial disproportions of a magnitude that affect both function and facial aesthetics.

Respiratory disability Obstructive sleep apnea, estimated to occur in between 5% and 10% of the western countries' population. Disabilities in the upper airway may affect the patient's general health and quality of life. Breathing incapability often lead to impaired sleep and consequently decrease the individual's overall capacity and performance. Known predisposing factors are obesity, smoking and age.

Treatment of respiratory disabilities Medical, behavioral and surgical treatment options are prospected methods and the treatment is individually planned in detail. The complex nature of obstructive sleep apnea may require multidisciplinary assessment.

Orthognathic surgery as treatment for obstructive sleep apnea syndrome (OSAS) Correction of anatomical abnormalities may cure obstructive sleep apnea or improve compliance with positive airway pressure treatment. Orthognathic surgery with an anterior movement of the jaws can increase the airway volume and facilitate breathing.

Measurements and evaluation of the upper airway volume Different methods of measuring the upper airway, like physio metric and radiological are present.

Project plan Subjects The study is performed retrospectively on a prospective material. Sixty-two consecutive patients aged between 18 to 30 years with Angle class III occlusion were included in the study.

Patients with systemic diseases in the musculoskeletal apparatus, drug abuse, poor psychic status or disease in the temporomandibular joint were excluded from the study.

Methods The study is performed retrospectively on a prospective material. Examination with clinical examination, BMI, HRQoL questionnaire, dental casts, photography and two- and three-dimensional radiographs and cephalometric measures was performed prior to surgery.

The patient's data (x-ray and photographs) were linked together in computer software programs and used for cephalometric analysis and simulation of the orthodontic and surgical movements (Fasad® and Simplant® PRO 12.00 OMS). The treatment was performed in accordance with this plan.

The last follow up was performed 12 months after surgery including identical registrations as prior to surgery, described above. HRQoL questionnaires consisted of Oral Health Impact Profile (OHIP-S), Jaw Functional Limitation Scale (JFLS-20) and Orofacial Aesthetic Scale (OAS-S). The results from the presurgical questionnaire will be compared with the postsurgical results. Twenty subjects were asked to fill in the follow-up questionnaire twice with two weeks interval for a reliability test of the method.

The pre- and postoperative CT will be compared in a software for measurements of upper airway volume with the software Philips IntelliSpace® Portal, version 11. Measures will be performed with an divided analysis of the upper airway according to the method described by Kim. Thus, the upper airway segmented into four compartments. The measurements will be performed on the sole segment volume and the total airway volume. A comparison of jaw movements, changes in airway volume, BMI and HRQoL will be performed.

Statistical methods The sample size, 62 patients, was based on numbers included in previous similar studies from other centers.

Simple statistics, mean and standard deviation (SD), for all variables will be used. Differences in airway volume and movements, preoperatively and postoperatively will be compared with McNemar's-test. Wilcoxon's paired-sample test will be used for analyzing airway volume before and after surgery as a numeric variable. The reliability test, performed as a test-retest, will be analyzed with the intraclass correlation coefficient, Fisher's test for pair comparisons and Pearson's correlation coefficient. Mann-Whitney-test will be performed to detect differences between questionnaire responses and clinical findings, i.e. BMI, and volumetric findings. The data will be assessed by using Spearman correlation analysis and simple linear regression analysis. Two-sided tests and alpha level 0.05 will be used. Confidence interval (CI) will be calculated. For all computations IBM® SPSS® statistical software will be used.